Comparing and matching curling stones and comparing sweeping brooms and the effects of brushing are important factors in the sport of curling. The quality of the ice surface is also important. Heretofore, however, efforts to make meaningful comparisons have been hampered because there is no known method or apparatus for ensuring that each stone is propelled down the ice with exactly the same force. At best, human throwers attempt to propel each stone using as consistent a throwing force as possible. Such an approach is clearly suspect and does not provide sufficient accuracy for comparative research purposes. Attempts have also been made to launch curling stones down sloping ramps or to hit a stone with the ball of a pendulum, but these attempts are not entirely satisfactory or accurate enough for research purposes.
Mechanical launching devices for propelling bowling balls, marbles, hockey pucks and the like are, of course, well known and generally rely on spring-loaded guns or are cable transmitted pusher devices such as that shown in U.S. Pat. No. 3,608,211, issued 28 Sep. 1971, for a launching device for demonstrating collision principles. A curling stone, however, weighs approximately forty-four pounds and spring-loaded guns capable of handling such a load are extremely cumbersome and difficult to load manually. There is a need, therefore, for a simple propelling device for curling stones and the like which applies a consistent propelling force every time it is used so as to provide a consistent "stone throw" which can be used to compare any of: individual stones, ice surfaces, efficiency of sweeping, broom design and other variables in the sport of curling.